Fish ranching—where the animals are free to roam but trained to return to a certain point so they can be caught—could one day become a significant part of global fisheries, fitting between traditional catching and aquaculture, says Björn Björnsson, the lead author of a study published in Marine Policy. (1) It could even reduce the catching of fish that are not the target species or are undersized.

“Ranching” allows fish to roam free but attempts to condition their behavior so they can be rounded up for feeding and eventual capture. Some researchers are experimenting with sound signals that condition the fish to return to feeding stations. But Björnsson’s economic analysis is based on a simpler method by which otherwise wild fish are conditioned by regular feeding at specific feed stations.

Based on data from an experiment conducted off the coast of Iceland in 2005–2006, Björnsson estimates that ranching is the most profitable way of putting cod on dinner plates. A typical fishing boat could make a profit of €71,000 (US$103,000), through traditional fishing, for 200 metric tons of cod. But the same boat, involved in cod ranching, could bring in more than 361 metric tons of cod with a net profit of €150,000.

Rather than indiscriminately netting all fish in the vicinity of the target animals, training a herd to respond to stimuli means fishermen could take just the species they were after when they were the right size.

Previous efforts at fish ranching have met with limited success. In the U.S., even preliminary experiments with ranching—using sound as a herding signal—attracted a lawsuit over fears that feeding the animals could cause pollution and disrupt ecosystems.

However, fisheries scientist Ray Hilborn at the University of Washington in Seattle notes that the method used in this study differs from other types of fish ranching. “The traditional approach is to hatch the juvenile fish in hatcheries, have them go, and have them come back,” he says. “[What Björnsson and his team] are really doing is using feed to aggregate fish.”

Scott Lindell, director of the Scientific Aquaculture Program at the Marine Biological Laboratory in Woods Hole, Massachusetts, notes that previous efforts at ranching have been scuppered by political and social arguments about who has jurisdiction over the fish. “It’s feasible, but it requires as much social engineering as it does anything to do with fish,” he says.